Re: problems with flips/rotations of certain shapes

From: Bob Powell [MVP] (bob_at__spamkiller_bobpowell.net)
Date: 01/08/05 

Date: Sat, 8 Jan 2005 02:14:49 +0100

Always draw as if you were drawing to an untransformed graphics device. The
matrix you use should always be fresh. That is to say that if you're drawing
is rotated 90 degrees and flipped horizontally then do hat every time you
draw. Dont rotate 90 degrees in one cycle and then flip horizontally in the
next.

Matrices can be compounded by multiplying them together. The order in which
you multiply is important. 

-- 
Bob Powell [MVP]
Visual C#, System.Drawing
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<sean.slavin@wonderware.com> wrote in message 
news:1105138006.490959.142200@f14g2000cwb.googlegroups.com...
> I'm trying to debug some code and now I'm lost. Here's the problem.
>
> I have a graphic editor with which I can draw shapes and other
> graphical items. I can also do rotations (90 degree increments,
> clockwise and counterclockwise) and flips (horizontal and vertical).
> With some shapes, such as a curve, they 'walk' across the screen as
> they are being rotated or flipped. Rotation and flips are being
> accomplished with a matrix. There is no apparent pattern to the
> 'walking'. Sometimes they move only 1 in the x and y directions.
> Sometimes more depending on how I've tried to compensate. I just can't
> seem to put a definitive finger on where this is happening.
>
> As far as I can tell, the calculation for determining the shapes
> bounding rectangle is off a little. I'm not sure why this occurring.
> I'm hoping that someone has had experience with this type of problem.
>
> If my explanation is lacking, please let me know and I'll do my best to
> explain further. I'm not sure if I can supply sample code but I might
> be able to come up with a snippet if need be.
>
> Thanks in advance
>
> Sean
>

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